1. Field of the Invention
This invention relates to a speed meter system for a vehicle, and more particularly, to a speed meter system which eliminates problems resulting from accumulated errors.
2. Description of the Prior Art
In prior art vehicle speed meter systems as shown in FIG. 1, for example, a pulse signal, generated by a pulse signal generating means a, corresponding to a vehicle speed is counted a predetermined period of time by a first counter b, and then the counted value thereof is applied to a second counter c. The number of pulse signals according to a vehicle speed is then counted for a subsequent current predetermined period of time by the first counter b, and then, the counts in counters a and b are compared in comparator d and a judgement signal indicating which of the counted signals is larger, is generated as a pulse difference signal by the comparator d. During the next predetermined period of time, that is, during the time that a new pulse signal corresponding to a vehicle speed is being counted by the first and second counters b, c, the comparison signal generated at the comparator d is applied to a memory e, and a standard pulse signal corresponding to the signal applied to memory e is generated from the memory e and applied to a pulse motor f to cause the motor to turn in a forward direction or a reverse direction, so that a pointer of an indication meter g coupled to the motor f indicates the measured value.
This conventional speed meter, however, is so arranged that the movement of the pointer of the speed meter g corresponds to a resultant value obtained by subtraction between the counted value of the first counter b and the counted value of the second counter c. Therefore, it has the disadvantage that if there is an error in counting by either of the two counters b or c, this error cannot be eliminated and remains in the counters b and c, and thus, at each time when an error is generated, the errors are accumulated in the resultant counted value.
Additionally, since the prior art speed meter system uses the pulse difference signal as the output of the comparator d, a large number of connecting lines, corresponding to the number of pulses, are required for connections between the comparator d and the memory e. This results in the disadvantage that the system has a high frequency of trouble and is expensive.